Work, Energy and Power comprehensive notes

WORK, ENERGY & POWER

Work

 Work done on an object by a constant force, F, is F∆xcosθ where
F is the magnitude of the force, ∆x the magnitude of the
displacement and the angle between the force and the
displacement
 W=F ∆x cosθ
 The amount of work done in Joules = amount of energy transferred

 Work is done on an object when the object moves in the same
plane as the force.
 If a force is applied to an object at 90o to the motion of the object
then that force does no work on the object.
 When a force is applied at an angle (θ) to an object then then work
is done by the component of the force that causes the object to
move.
 This is given by the following equation: 𝑊 = 𝐹Δ𝑥𝑐𝑜𝑠 𝜃 W = work
done (J)
o F = force applied (N)
o Δx = displacement (m)
o θ = angle of force to the direction of motion
 Work is a scalar quantity therefore it has magnitude but not
direction.
 Work can be a negative value when the energy of the system
decreases and positive when the energy of the system increases.

Positive Work
 Energy is transferred to the body increases energy of system
 Depends on the angle between the force and the displacement
 cos< 90°

Negative Work
 Energy is transferred from the body decreases energy of system
 Force is acting against the motion of the object, slowing it down
removing energy
 90° < cos 180°

Zero Work
 No work is done on an object when:
1. F = 0 N
2. x = 0 m